In copending application Ser. No. 503,178 filed June 10, 1983, now U.S. Pat. No. 4,501,721 (the disclosure of which is hereby incorporated by reference herein), a method was provided for removing predetermined constituents from a particlized mineral material, such as removing precious metals from a metal bearing ore. The invention disclosed therein is extremely useful for removing metals from many types of ores, however it is not particularly applicable to recovery of materials from refractory ores.
Refractory ores are those in which metal cannot be easily leached since it is held by chemical bonds or locked inside mineral particles. Often, the metal is bound with sulphur. A typical refractory ore is gold ore in which the gold is disseminated in iron sulfide. Other refractory ores are those containing aluminum (i.e. bauxite), and some nickel, cobalt, zinc, uranium, copper ores (i.e. chalcopyrite), and the like. Pressure hydrometallurgy has been successfully employed for effecting metal recovery from refractory ores. However conventional pressure hydrometallurgical processes are energy intensive since a large amount of heat is wasted in grinding of the ore prior to actual leaching, and such processes often consume substantial amounts of chemicals, such as lime for the neutralization of sulphuric acid which is formed when the metal-sulphur bonds are broken in the refractory ore.
According to the present invention, a pressure hydrometallurgical processes is provided which has numerous advantages over prior art processes for ultimately effecting metal removing from refractory ores. According to the present invention on continuous process is practiced, with careful heat recovery steps being implemented, so that the energy requirements are very substantially reduced compared to conventional pressure agitation and like processes. Also, according to the present invention continuous washing is effected of the refractory ore after the metal-sulphur bonds have been broken, so that no lime--or like chemical--need be consumed to neutralize the sulphuric acid and the like produced during oxidation, and in order to even allow acid recovery.
According to one aspect of the method according to the present invention, a method of removing metal from a particlized metal bearing refractory ore (one in which the metal is bound chemically, usually with sulphur) is provided. The method comprises the following steps:
(a) Mixing the particlized refractory ore with a heated liquid to form a heated liquid slurry.
(b) Continuously passing the slurry in a flow path.
(c) Oxidizing constituents of the ore in the slurry while in said flow path, at super atmospheric pressure and temperature above 212.degree. F.
(d) Washing the ore in the slurry with a wash liquid to remove products of oxidation therefrom.
(e) Recovering heat from the slurry, including as part of step (d); and
(f) subsequently effecting leaching of the washed, oxidized, particlized refractory ore, to effect recovery of metal therefrom.
In the practice of the invention, as in the practice of the method disclosed in said copending application Ser. No. 503,178, it is highly desirable to add flocculant and/or fibers to the slurry during mixing. The flocculant and fibers hold the particlized ore in a stable network in the slurry. The flocculant may be a natural or synthetic polymer such as a synthetic polymer of anionic, cationic, or nonionic type. The fibers may be cellulosic, fiberglass, or ceramic fibers (or mixtures thereof), and preferably the fibers make up about 0.01-10% by weight of the slurry.
According to another aspect of the present invention, a method of removing metal from a particlized metal bearing ore is provided which comprises the following steps:
(a) mixing the particlized refractory ore with a heated liquid to form a heated liquid slurry.
(b) Continuously passing the slurry to a top portion of the first vessel, and flowing the slurry downwardly in the first vessel.
(c) Introducing heated liquid containing an oxidizing agent into the bottom of the first vessel to flow countercurrently to the slurry flowing downwardly in the first vessel.
(d) Removing treated slurry from the bottom of the first vessel and passing it to a top portion of the second vessel so that it flows generally downwardly in the second vessel.
(e) Removing liquid from adjacent the top of the first vessel, and circulating that liquid to the bottom of the second vessel to flow in the second vessel generally countercurrently to the slurry flowing downwardly in the second vessel.
(f) Removing liquid from the second vessel adjacent the top thereof.
(g) Removing treated slurry from the bottom of the second vessel and passing it to a top portion of the third vessel so that it flows generally downwardly in the third vessel.
(h) Introducing wash water into the bottom of the third vessel so that it flows generally countercurrently to the slurry flowing downwardly therein.
(i) Removing spent wash liquid from adjacent the top portion of the third vessel; and
(j) removing washed slurry from the bottom of the third vessel and subsequently effecting leaching treatment thereof so as to remove metal from the metal bearing refractory ore.
In the practice of this particular method, it is desirable to add oxygen (or like oxidizing agent) to the liquid removed from the first vessel before introduction into the second vessel, and to add oxygen to and heat the liquid removed from the second vessel, and then introduce it as the countercurrent flowing liquid at the bottom of the first vessel. The temperature of the liquid introduced at the bottom of the first vessel is preferably generally about 330.degree. F. Flocculant and fibers prferably are added to the slurry during mixing.
It is the primary object of the present invention to provide an effective, energy efficient, and economical method facilitating the recovery of metal from refractory ores. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.